(1) Field of the Invention
The invention is directed to a stop element for a hydraulic bearing, i.e., an elastomeric bearing with hydraulic damping. The invention is also directed to a hydraulic bushing, or an elastomeric bush bearing with hydraulic damping, with at least one radial stop, which can be implemented with the stop element of the invention.
(2) Description of Related Art
Elastomeric bearings of different designs are used in large numbers as axial and radial bearings (bush bearings) to provide oscillation-damping support of structural components of machines, industrial plants, vehicles and buildings. Depending on the application, the bearings formed with an elastomeric bearing body for improving the oscillation characteristic or for increasing the comfort are designed as hydraulic bearings, i.e., provided in addition with hydraulic damping. Elastomeric supports then include at least one work chamber disposed on or in the bearing body for receiving a fluidic damping means, wherein the work chambers are connected with one another for flow communication. If a load is applied in the region of one of the work chambers, then the damping means is displaced into the respective other work chamber, so that mass or throttle damping is provided depending on the geometry of a channel which connects the work chambers for flow conduction.
In particular in the construction of modern vehicles, the bush bearings or radial bearings employed predominantly for the chassis suspension are frequently implemented as hydraulic bushings. The hydraulic bushings generally consist of a preferably metallic, mostly cylindrical inner part, an elastomeric bearing body encompassing the inner part, and an outer sleeve receiving the inner part with the bearing body. At least two work chambers receiving the fluidic damping means are formed inside the bearing body or between the outer contour of the bearing body and the outer sleeve. The work chambers are mutually offset in the circumferential direction and connected by at least one channel.
In practical applications, in particular the chamber walls of such hydraulic bushing are subjected to high loads, because the bearing body absorbs the acting forces and provides damping predominantly by deforming the chamber walls.
To protect the bearing from destruction at high loads due to tearing chamber walls and subsequent leakage of the damping means, the deformation of the chamber walls must be limited. This is attained by forming radial limits stops in or on the bearing or the hydraulic bushing, respectively. The radial limits stops are implemented by forming radial protrusions on the outside of the inner part or on the inside of the outer sleeve, thereby forming a stop body which at high radial loads makes contact with a support surface which faces the stop body in the radial direction. The contact surfaces of both the stop body and the support surface are predominately implemented with the material pair combinations rubber/steel, rubber/aluminum, plastic/steel, plastic/aluminum. A corresponding hydraulic bushing with radial limit stops arranged outside its wall chambers containing the fluidic damping means is described, for example, in DE 38 18 287 C2. Conversely, DE 197 17 210 A1 describes a hydraulic bushing with radial stops arranged in the work chambers of the bushing.
If high radial loads act on the elastomeric bush bearing and the oscillations causing the loads also have a high frequency, which happens with shock-like loads, then the bearing body, in particular the chamber walls, encounter high deformation speeds. The radial stops are mainly employed to absorb high radial loads which simultaneously cause torsional and gimbal excursions of the hydraulic bearing. High surface pressures are accompanied by relative movements between the loaded contact surfaces constructed of the aforementioned materials. If the radial stops are provided with a rubberized surface, then the aforedescribed relative movements causes high abrasion at large excursions, because of the rigid connection between the limit stops and the respective base body. On the other hand, small excursions may produce noticeable and annoying noise. Moreover, when the corresponding bearing components strike the stop body, the force transmission of the bearings disclosed in the aforementioned documents becomes abruptly progressive.
However, it is desirable for improving the comfort to dampen the limit stop so that the surface areas of the bearing elements, which come into contact with the stop bodies, do not stop abruptly, but gradually depending on the deformation speed. Accordingly, instantaneous damping of the actual forces and a slow progression of the counterforces produced by these forces in the bearing is desired. For this reason, elastomeric bearings, in particular hydraulic bushings, have been disclosed where in the limit stop(s) is/are also hydraulically damped. A hydraulic bushing of this type is described in DE 196 26 535 A1. In the bush bearing described in this document, the otherwise cylindrical inner part has a rubberized outer surface and in the region of the work chambers a corresponding bulge. A V-shaped depression is machined in each of the bulges. A stop body formed as a truncated cone is inserted into the depression, which floats on a fluid film which is formed by the damping means from the work chamber and disposed between its outer surfaces and the outer surfaces of the depression. Accordingly, a small channel for the damping means is formed between the stop body operating at a displacement body and the outer surfaces of the depression. This initially provides basically a good impact damping. However, the relatively large rubber surfaces on the legs of the V-shaped depression have proven to be a disadvantage. It has been observed that the rubber of the bearing body covering the depression is subjected to heavy wear. In addition, the narrowness of the channel below the stop body allows the desired damping characteristics to be adjusted only within certain limits.